Electrolytic hydrodimerisation process

ABSTRACT

A,B-ETHYLENIC COMPOUNDS ARE HYDRODIMERISED, FOR EXAMPLE ACRYLONTRILE IS CONVERTED INTO ADIPONITRILE, WITH REDUCED FORMATION OF BY-PRODUCTS BY ELECTROLYSIS IN A SINGLE COMPARTMENT OF A HOMOGENEOUS AQUEOUS SOLUTION OF THE ETHYLENIC COMPOUND AND A QUATERNARY AMMONIUM SALT OF AN OXIDIZED MINERAL ACID WHICH DOES NOT INTERFERE IN THE REACTION, THE CONCENTRATION OF THE ETHYLENIC COMPOUND BEING 2.3 TO 4.6% BY WEIGHT.

United States Patent 3,630,861 Patented Dec. 28, 1971 Int. Cl. C07b 29/ 06; C07c 121/26 US. Cl. 204--73 A 2 Claims ABSTRACT OF THE DISCLOSURE u,fl-Ethylenic compounds are hydrodimerised, for example acrylonitrile is converted into adiponitrile, with reduced formation of by-products by electrolysis in a single compartment of a homogeneous aqueous solution of the ethylenic compound and a quaternary ammonium salt of an oxidized mineral acid which does not interfere in the reaction, the concentration of the ethylenic compound being 2.3 to 4.6% by weight.

The present invention relates to the electrolytic hydrodimerisation of O B-ethylenic monomers, more particularly acrylonitrile.

Various electrolytic hydrodimerisation processes for ethylenic compounds as aqueous solutions have already been proposed. Thus, a,fi-ethylenic ketones, and unsaturated compounds such as coumarin, stilbene and acrolein have been hydrodimerised by electrolysis in aqueous medium, optionally in the presence of a co-solvent [see Wilson, Trans. Electrochem. Soc. 80, 139 (1941) and 84 153 (1943); Pasternak, Helv. Chem. Acta 31, 753 (1953); Knouniants, Usp. Khim. 23 (7) 781-820 (1954); Tomilov, Russian Chem. Rev. 32, 36-37].

It has been proposed in French Patent No. 1,328,327 to carry out the electrolytic hydrodimerisation of ,5- ethylenic compounds, and particularly of acrylonitrile to adiponitrile (which is an intermediate product of particular importance in the manufacture of polyamides), by electrolysis of their aqueous solutions containing a support electrolyte. A characteristic of this process consists in the use of aqueous electrolytic baths, in which the concentration of monomer is at least 10% by weight. According to the process of this patent, during the electrolysis of aqueous solutions of c p-ethylenic compounds there are two secondary types of reactions: reduction and condensation. With acrylonitrile in particular, as well as the dimerisation reaction, reduction of the acrylonitrile to propionitrile, and a condensation with the formation of bis-(2-cyanoethyl)-ether, can also take place.

Although these reactions take place more or less simultaneously, the extent thereof varies according to the concentration of the olefine in the electrolysis solution. Thus, in the case of acrylonitrile, the formation of propionitrile increases when the concentration of acrylonitrile de creases. The aforementioned French patent states that when the concentration of the acrylonitrile changes from 40% to 20%, the yield of propionitrile changes from to 10%. When the concentration of the acrylonitrile falls to the quantity of propionitrile formed represents more than a third of the product resulting from the electrolysis. To obtain the concentrated acrylonitrile solutions which are considered essential according to this patent, it is necessary to make use of support electrolytes which act as hydrotopic salts favouring the dissolution of the acrylonitrile in water. The salts which best satisfy this double requirement are the salts of sulphonic acids, the

cations of which are not discharged at the voltages used in the hydrodimerisation, and particularly the quaternary ammonium sulphonates.

However, even if these salts are particularly suitable for carrying out the process described in this French patent, it has been observed that the majority of the most interesting of the said salts, and particularly the aryl sulphonates, are oxidised at the anode under the concentration conditions used (see French Patent No. 1,415,524). Furthermore, it has been found that acrylonitrile also undergoes an anodic oxidation (see French Pats. Nos. 1,415,524 and 1,401,175). These anodic oxidation phenomena are shown by a loss of acrylonitrile and of support electrode, with the formation of oxidation products which cause a chemical attack on the anode. To avoid these disadvantages, it is essential to separate the anode and cathode compartments by a diaphragm (a porous body or ion exchange membrane) to prevent the passage of the anions and acrylonitrile from the cathode compartment into the anode compartment.

However, the use of diaphragms is not without disadvantages. In fact, their presence in the electrolysis medium increases the resistance of the cell and leads to an additional consumption of energy. Moreover, to limit the energy loss caused by the Joule effect, it is desirable to arrange the electrodes as close as possible to one another, and the presence of a diaphragm makes this arrangement more difficult to achieve on a technological scale (because of, e.g. the need to provide spacers to maintain a constant spacing between the electrodes and the diaphragm, and the need to control the pressure exerted on each face of the diaphragm).

The present invention provides a process for the hydrodimerisation of a,5-ethylenic compounds by electrolysis in a cell without a diaphragm, by which it is possible to obtain simultaneously excellent chemical and electrical efiiciencies, in relation to the hydrodimerisation product. This process consists in subjecting to electrolysis, in a single compartment cell, a homogeneous aqueous solution of an a,,B-ethylenic compound and an electrolyte consisting of a quaternary ammonium salt of an oxidised mineral acid, which cannot be oxidised or reduced under the electrolysis conditions into a product capable of harming the reaction, the concentration of the a,fi-ethylenic compound in the reaction medium being below 10.5% by weight, and preferably below 5% by weight.

This new process makes it possible to limit and even avoid the anodic oxidation of the ethylenic compound, while simultaneously limiting the formation of dihydrogenated compounds. It has been found that the importance of the anodic phenomena decreases with the concentration of the olefine in the bath, and becomes practically zero for concentrations below 5%. Thus, in the case of the electrolysis of aqueous solutions of acrylonitrile containing less than 5% of acrylonitrile, the chemical and electrical yields of adiponitrile are raised to and higher, and the ratio of the adiponitrile to the propionitrile produced from the process remains between 10:1 and 40:1 in the majority of cases, the exact ratio depending on the reaction conditions. This is an unexpected result, since according to the prior art, this ratio falls to about 1.711 when the concentration of acrylonitrile in the electrolysis medium is 5%. In practice, although it is possible to operate on solutions having an acrylonitrile concentration as low as 0.5%, there is no advantage in using solutions with a concentration below 1.5%.

The electrolyte employed in the new process is a quaternary ammonium salt of the formula:

t) a f N in which A represents the anion of an oxidised mineral acid as hereinafter defined and R R R and R represent identical or different hydrocarbon radicals each comprising 1 to 20 carbon atoms in their chain.

More specifically, the anion A is chosen from thos which are not oxidised at the anode or reduced at the cathode under the reaction conditions, or which do not give harmful products when anodically oxidized. Among the non-oxidisable or reducible anions derived from oxidised mineral acids, it is preferred to use the sulphate, borate, phosphate and carbonate anions. It is also possible to use anions oxidisable at the anode without the formation of corrosive products; thus, the bisulphite anion, oxidised at the anode into the sulphate ion, can be used, although there is not particular advantage in so doing.

In the above-given formula, R R R and R, can be linear or branched alkyl radicals, such as methyl, ethyl, propyl, butyl, isopropyl, pentyl, hexyl, heptyl, octyl, dodecyl, and 2-ethylhexyl; cycloalkyl or alkyl-cycloalkyl radicals, such as cyclohexyl; or aryl radicals such as phenyl. Thus suitable cations are tetrabutyl-ammonium, triethyl- (n-octyl) ammonium, triethyl (n-dodecyl)-ammonium, tetra-(n-pentyl)-ammonium, tetraethyl-arnmonium, tetra- (n-propyl)-ammonium, methyl-triethyl-ammonium, triethylbutyl-ammonium, triethylhexyl-ammonium, and triethyl- (2-ethylhexyl)-ammonium.

Suitable quaternary ammonium salts which are particularly well suited for carrying out the process of the invention, are the sulphates, borates, phosphates and carbonates of tetra- (n-butyl -amrnonium, tetran-pentyl -ammoniurn, triethyl-(n-dodecyl) ammonium, triethyl-(n-octyD- ammonium, triethylhexyl-ammoniurn and triethyl-(Z- ethylhexyl)-ammonium.

The concentration of the electrolyte in the electrolysis bath should be at least and preferably should be between 10 and by weight, related to the total mixture.

Instead of carrying out the new process in a purely aqueous medium, it is also possible to use, concurrently with the water, inert solvents such as dimethylformamide, dimethylacetamide, dimethylsulphoxide, dioxane, diethylene glycol, ethanol, hexamethylphosphotriamide and acetonitrile.

To ensure a normal progress of the hydrodimerisation and to avoid the preponderant formation of by-products such as propionitrile, B-hydroxypropionitrile or bis-(ficyanoethyl)-ether, it is desirable to keep the pH of the electrolysis medium between 5 and 10. When the anion of the quaternary ammonium salt used as electrolyte is derived from a weak acid, and particularly when using acid salts of which the pK is between 5 and 11, the pH of the aqueous solution is generally higher than 10. It is appropriate in this case for the solution to have added thereto an acid in a quantity sufficient to bring the pH of the solution within the preferred limits. To achieve this object, it is preferred to use an acid of which the anion cannot be oxidised at the anode. The use of acids corresponding to the anions of the quaternary ammonium salts being used is particularly suitable. A buffer system is then formed in the aqueous electrolysis solution, e.g. the system quaternary ammonium borate/boric acid, quaternary ammonium carbonate/bicarbonate, and quaternary ammonium monobasic phosphate/dibasic phosphate, which enables the pH to be maintained between the preferred values throughout the entire reaction. The buffering effect is at its maximum when the basic form and the acid form are in equal concentrations. Nevertheless, these proportions can be changed, if it is desired to have a pH other than that corresponding to the pK of the pair, without however one of the forms being in too great an excess with respect to the other. In general, the best results are obtained when the acid form represents to 75% of the concentration of the salt.

One convenient method for obtaining the aqueous buffer systems consists in adding to an aqueous solution of a quaternary ammonium hydroxide of selected concentration an acid such as boric, phosphoric or carbonic acid, until the pH of the solution is close to the pK of the buffer pair.

The temperature of the reaction medium can vary between 0 and the reflux temperature of the medium. Generally, a temperature between 20 and 45 C. is used.

The electrodes can be made of any metal or alloy generally employed in connection with electrolysis and suitable in view of the chemical nature of the compound subjected to the electrolysis. Thus, the cathode should be formed of a material which does not permit water to be reduced at the voltage used for the reduction of the 04,3- ethylene compound. Mercury, graphite, lead, lead/mercury and lead/ antimony alloys, Darcet alloy, tin and zinc are among the materials which fulfil this condition. Mercury, lead and graphite are particularly suitable. The anode should be made of a metal or metal alloy which provides a slight oxygen over-voltage in the electrolysis of water, such as, for example, lead, which may or may not be covered with oxide, nickel, which may or may not be surface-oxidised, platinum, gold, and stainless steel, which is preferably passivated. It is preferred to use insoluble anodes which have an oxygen over-voltage smaller than that of gold.

The voltage applied to the terminals of the electrolysis cell can vary within wide limits. It is generally unnecessary to make use of high voltages and voltages between 3 and 8 volts are generally quite suitable. To minimise the ohmic voltage drop and correlatively the energy loss due to the Joule effect in the electrolyte, it is possible to reduce the distance of the electrodes. This distance or spacing is not critical, but in order to ensure a good circulation of the liquid between the electrodes, it can with advantage be between 1 and 15 millimetres and preferably between 1 and 3 millimetres.

The current density is not critical and can consequently vary within very wide limits. In general, the productivity of the installation is higher as the current density is higher. It is possible to work at current densities which are from 1 to 50 amperes/dmF, and preferably 1 to 10 amperes/ dm. Although the speed of circulation of the electrolysis bath can assume extremely different values, it is preferable to have high circulation speeds. Speeds which are between 5 cm./sec. and 2 m./sec., and preferably between 10 and cm./sec., are very suitable.

The process according to the invention can be applied to any a,fi-ethylenic compound, such as nitriles (e. g. acrylonitrile and methacrylonitrile), aldehydes (e.g. acrolein and methacrolein), acrylates and methacrylates, and acrylamides and methacrylamides.

The product of the electrolysis is a homogeneous aqueous solution. The products formed during the reaction can be isolated, e.g., by distillation and solvent extraction. One particularly convenient separation method consists in lowering the temperature of the reaction mass to a smallest possible value at which it remains liquid in order to cause a lowering of the solubility of the organic compounds in the saline aqueous phase. An organic phase then generally forms comprising the major part of the reaction products. The aqueous phase containing the major part of the untransformed monomer can be used again as electrolysis bath after addition of monomer until the desired concentration is obtained.

The process which forms the subject of the present invention is very suitable for being carried out continuously.

The following examples illustrate the invention. In these examples, the expression electrical yield is issued in the usual way to indicate the percentage which represents the quantity of electricity theoretically necessary to preparing the stated amount of the desired product, com pared with the quantity of electricity actually used in the experiment.

EXAMPLE 1 The apparatus employed is formed by an electrolysis cell connected by a glass pipe, on the one hand, to an expansion chamber and, on the other hand, to a circulating pump which is itself connected to the expansion chamber. The electrolysis cell is formed by two square metal plates, each with an area of 1 dm. and a thickness of 1 mm., separated on their periphery by a silicone resin joint with a thickness of 3.5 mm. Each metal plate is covered externally by a plate of plastic material. The tightness of the assembly is ensured by clamping with bolts. One of the metal plates consists of hard lead (lead/antimony alloy with of antimony). The other plate consists of pure lead. The two electrodes are connected to a direct current source. The hard lead plate serves as anode and the pure lead plate as cathode.

Each plate contains an orifice, one of which serves for the entry of the electrolytic solution into the space between the electrodes and the other for the discharge of the said solution.

The outlet orifice of the electrolysis bath is connected to the expansion chamber formed by a container comprising a double jacket, in which cold water is circulating. This container has arranged above it a cold water condenser, above which is a condenser with a mixture of acetone/ solid carbon dioxide. A graduated burette opens into the expansion chamber. The solution leaving the expansion chamber is returned by the pump into the cell.

Prior to the electrolysis, the hard lead anode is formed by filling the cell with 5 N-sulphuric acid and causing a current of amperes to flow for 15 minutes. The cell is then emptied and rinsed with distilled water.

Into the expansion chamber as described above, 370 g. of an aqueous solution of 15% by weight of triethyl-(noctyl)-arnmonium hydroxide are introduced, and then 40 g. of boric acid are added. In this manner, a solution is obtained of pH 8.7. 74.1 g. of acrylonitrile are introduced into the burette placed above the expansion chamber. 16 cc. of this acrylonitrile are introduced into the aqueous solution. A solution is obtained which comprises 3% by weight of acrylonitrile. The temperature of this solution is brought to C. and this temperature is maintained throughout the experiment. The solution is introduced into the cell at the rate of 250 litres/hour (linear speed: 20 cm./sec.). Simultaneously, a mean voltage of 7.2 volts is applied to the terminals of the cell so as to maintain a current of 5.2 amperes. The quantity of current passing through the cell is measured by means of an integrating apparatus.

To keep the acrylonitrile concentration of the bath close to the initial concentration, 2 cc. of acrylonitrile are poured in every 2910 coulombs.

After having maintained these conditions for 6 hours, the current is stopped and the reaction mass is cooled to 15 C.; the solution obtained is pale yellow and h0- mogeneous.

The quantity of electricity used during the reaction is 113,500 coulombs (i.e. 31.5 ampere-hours).

Hydrochloric acid is added to the reaction mass until the pH is 7. The solution is drawn 0E and the apparatus rinsed with 100 cc. of dimethyl formamide. The solution obtained is distilled at normal pressure until the temperature of the vapours reaches 100 C. The distillate which is obtained comprises two phases. Dimethyl formamide is then added until the two phases are miscible. The colourless solution obtained (265.2 g.) is analysed by vapour phase chromatography. It contains 14.05 g. of acrylonitrile and 3.8 g. of propionitrile.

The residue from the distillation is concentrated at C. under a vacuum of 15 mm. Hg. After cooling to 20 C., the boric acid precipitate formed is filtered off and washed with 20 cc. of acetonitrile. A filtrate of 281.6 g. is thus obtained, containing 19.3% of adiponitrile (i.e. 54.4 g.) measured by vapour phase chomatography.

g. of this filtrate are extracted seven times with 100 cc. of methylene chloride. The combined extracts are washed three times with 100 cc. of water so as to eliminate all trace of chloride ion.

The extract, thus treated, is dried over anhydrous sodium sulphate, filtered, and distilled in vacuo. 1.4 g. of a fraction distilling between and C./ 0 .1 mm. Hg are collected in this way. The distillation residue is 0.3 .g.

Analysis shows that the fraction which has distilled is formed by the hydrotrimer of acrylonitrile viz 4-cyanosuberonitrile. (By alkali hydrolysis, this compound is transformed into 4-carboxy-suberic acid, M.P. 111 C. after recrystallisation from a mixture of acetic acid and benzene.

The balance of the reaction is as follows:

(1) Chemical yields with respect to acrylonitrile used up:

Percent Adiponitrile 88.9

Propionitrile 6.1

Hydrotrimer 4.3 (2) Electrical yields:

Adiponitrile 85.5

Propionitrile 11.7

Hydrotrimer 2.8 (3) Ratio by weight of adiponitrile/propionitrile: 14.3: 1.

EXAMPLE 2 The experiment is carried out in the apparatus used in Example 1 and with an electrolytic solution obtained in the same manner, but in which the concentration by weight of acrylonitrile is 4.3%. This concentration is kept substantially constant throughout the operation.

The current density is 7.8 amperes and the applied voltage is 9.5 volts. The operation is continued until 31.5 ampere-hours have passed through the cell. The rate of circulation is 600 litres/hour. The quantity of acrylonitrile used is 79.9 g.

The reaction mass is treated as in Example 1. The balance of the reaction is as follows:

G. Acrylonitrile not transformed 14.2 Propionitrile formed 1.4 Adiponitrile formed 57 Hydrotrimer formed 5 Chemical yields Percent Adiponitrile 85 Propionitrile 2 Hydrotrimer 7.6

, Electrical yields Percent Adiponitrile 89.5 Propionitrile 4.2 Hydrotrimer 3.7

Ratio by weight of adiponitrile to propionitrile: 40.7 :1.

EXAMPLE 3 An electrolytic solution is prepared by causing a stream of carbon dioxide gas to pass into 400 g. of a 15% by weight aqueous solution of triethyl-(n-octyl)-ammonium hydroxide until a pH of 9 is obtained. Using the apparatus described in Example 1, electrolysis is carried out under the following conditions:

Initial concentration of acrylonitrile in the solution percent by wt. 4.3 Applied voltage volts 5 Current intensity amperes 5.4 Temperature c C 34 Circulation rate of the solution litres/hour 250 7 After treatment of the reaction mass as in Example 1, the balance of the reaction is as follows:

Adiponitrile formed 50.1

Hydrotrimer formed 3.5

Chemical yields Percent Adiponitrile 81.5

Propionitrile 7.7

Hydrotrimer 5.6

Electrical yields Percent Adiponitrile 79 Propionitrile 14.8

Hydrotrimer 3.6

EXAMPLE 4 The experiment is carried out in the apparatus described in Example 1, but with an electrolyte solution obtained by passing carbon dioxide gas into 400 g. of a 15% by weight aqueous solution of tetra-(n-butyl)- ammonium hydroxide until a pH equal to 9 is obtained.

The electrolysis is carried out under the following conditions:

Initial concentration of acrylonitrile in the solution percent 4.45 Final concentration of acrylonitrile percent 3.4 Current density amps/dm. 5.4 Voltage volts 5.2 Circulation rate of the solution litres/hour 250 Quantity of electricity used amperehours 31.5 Total quantity of acrylonitrile employed g 79.6 Temperature C 34 The reaction mass is treated as in Example 1. The balance of the operation is as follows:

The operation is repeated with an electrolyte solution obtained in the same way, but with passage of CO continued until a pH equal to 7.5 is obtained. All the other conditions being identical (the voltage being however 6.2 volts), the following yields are obtained:

Chemical yields Percent Adiponitrile 80.8 Propionitrile 5.5

Electrical yields Percent Adiponitrile 83 Propionitrile 11.3

EXAMPLES TO 7 The first experiment of Example 4 is repeated, the concentration of the acrylonitrile in the electrolysis bath and the current density being varied, but the other factors remaining identical with those of Example 4. The results which are set out in the following tables are obtained:

Coneen- Quantity tration of Current of elee- Products formed acrylonidensity trieity in in g.

trile, in Voltage ampcro- Ex percent amps./dn1. (volts) hours ADN PN HT Yields (percent) Chemical Electrical Ex. ADN PN HT ADN PN HT ADN =adiponitrile; PN =propiouitrile; HT=hydrotrimer.

By way of comparison, the following test was carried out, in which the same electrolytic solution as in Example 4 (350 g.) of an aqueous solution of the tetra-(n-butyl)- ammonium carbonate/bicarbonate system at pH 9 was used, but of which the concentration of acrylonitrile was brought to 17.1% by addition of 72.3 g. of acrylonitrile. This concentration is maintained throughout the operation by addition of 2 cc. of acrylonitrile every 2910 coulombs. The current density is 5 .6 amperes at 5 .6 volts. The reaction is continued until 31.5 ampere-hours have passed through the cell. The total quantity of acrylonitrile used is 133.3 g.

After treatment of the reaction mass as in the preceeding examples, there are recovered:

Acrylonitrile 54 Adiponitrile 56.3 Propionitrile 0 Trimer 9.65

The chemical yields are respectively 69.7%, 0% and 12.1% and the electrical yields are 89%, 0% and 10%.

It is found that on increasing the concentration of the acrylonitrile in the electrolysis bath, there is a lowering of the yield of adiponitrile with respect to the transformed acrylonitrile, although there is no formation of propionitrile. Part of the acrylonitrile introduced is lost. The electrical yields (89+10%) relating to the reaction at the cathode (formation of adiponitrile and hydrotrimer) show that the only appreciable electrochemical reaction at the cathode is the reduction of the acrylonitrile. Consequently, the acrylonitrile lost (18.2%) has been destroyed at the anode.

EXAMPLE 8 The experiment at pH 9 of Example 4 is repeated, but replacing the lead cathode by a cathode of lead amalgam. The following results are obtained:

Chemical yields Percent Adiponitrile 79 Propionitrile 11 Trimer 6.2

Electrical yields Percent Adiponitrile Propionitrile 21 Trimer 3.9

EXAMPLE 9 As electrolyte, 417 g. of an aqueous solution of triethyl- (n-octyl)-arnmonium monobasic phosphate/dibasic phosphate at pH 7, obtained by adding phosphoric acid to 400 g. of a 15% solution of triethyl-(n-octyl)-ammonium hydroxide, are used.

16 cc. of acrylonitrile (a concentration of 3%) are introduced into this solution. The electrolysis is carried out as in Example 1, with a current density of 5.65 amps/dm. at 5.4 volts. The rate of flow of liquid circulating in the bath is 450 litres/hour. The concentration of acrylonitrile is kept in the region of its initial value, as in the preceding examples. The reaction is stopped when the quantity of electricity which has passed through the cell is 31.5 ampere-hours. The quantity of acrylonitrile employed is 73.8 g.

After treatment of the reaction mass, there are recovered:

G. Acrylonitrile 16.7 Adiponitrile 49.5 Propionitrile 6.5 Trimer 1.9

The chemical yields are as follows:

Percent Adiponitrile 85 Propionitrile 10.9 Trimer 3.3

and the electrical yields are:

Percent Adiponitrile 73.3 Propionitrile 20 .2 Trimer 2.1

EXAMPLES 10 TO 12 The electrolyte used is obtained by adding boric acid to a 15% by weight aqueous solution of tetra-(n-butyl)-ammonium hydroxide until a pH of 9 is obtained.

A series of tests is carried out, at a temperature of 34 C., and a circulation rate of the solution of 250 litres/ hours, but in which the concentration of acrylonitrile and the current density are caused to vary. The results set out in the following tables are obtained:

Concen- Quantity tration of Current of elec- Products formed acrylonidensity trinity in in g.

trile, in ampsJ Voltage ampere- Ex. percent dm. (volts) hours ADN PN HT Yields (percent) Chemical Electrical Ex. ADN PN HT ADN PN HT ADN adiponitrile; PN propiom'trile; HT hydrotimer.

EXAMPLE 13 An electrolyte solution is prepared by causing a current of carbon dioxide to pass into a 15 aqueous solution of triethyl-(n-dodecyl)-ammonium hydroxide until the pH is 9. Electrolysis is carried out in the apparatus of Example 1, under the following conditions:

Concentration of acrylonitrile percent 4.6 Current density amps/dm. 6.5 Voltage volts 6.2 Temperature s C 30 Circulation rate of the bath litres/hour 250 Quantity of electricity ampere-hours 32 Quantity of acrylonitrile employed g 79.8

The balance of the reaction is as follows:

G. Quantity of acrylonitrile not transformed 23.7 Adiponitrile formed 45.6 Propionitrile formed 6.75 Trimer formed 2.5

10 Chemical yields Percent Adiponitrile Propionitrile 11.6 Trimer 4.5

Electrical yields Percent Adiponitrile 71 Propionitrile 20.6 Trimer 2.6

EXAMPLE 14 An electrolyte, a solution obtained by passing carbon dioxide into a 15% aqueous solution of tributyl-(n-dodecyl)-ammonium hydroxide until a pH equal to 9 is obtained, is used.

The electrolysis conditions are those of Example 13 except as follows: The concentration of acrylonitrile is 2.3%. The current density is 4.35 amps/dmP. The voltage is 6.6 volts. The circulation rate is 450 litres/hour. The quantity of acrylonitrile employed is 50.3 g. The quantity of electricity is 21.8 ampere-hours.

The balance of the reaction is as follows:

Quantity of acrylonitrile not transformed 11.8

Adiponitrile formed 31.3

Propionitrile formed 3.5

Chemical yields Percent Adiponitrile 79.9

Propionitrile 8.75

Electrical yields Percent Adiponitrile 71 Propionitrile 15.6

EXAMPLE 15 The electrolyte solution is obtained by adding boric acid to a 15% aqueous solution of tetra-(n-pentyl)-ammonium hydroxide until a pH equal to 9 is obtained.

The electrolysis is carried out as in Example 14, but at a current density of 5.3 arnps/dm. (voltage of 7.8 volts). The quantity of electricity used is 31.5 amperehours and the quantity of acrylonitrile employed is 70.1 g., for a concentration kept between 2.9 and 2.4%.

The balance of the reaction is as follows:

418 g. of the solution prepared in Example 1 and to which has been added 16 cc. of acrylonitrile (a concentration of 3%) are used. This concentration is maintained during the reaction by addition of acryonitrile. The reaction conditions are those of Example 1. Altogether, 90.2 g. of acrylonitrile and 40 ampere-hours of electricity are employed.

On completion of the reaction, a homogeneous solution is obtained, which is cooled to 4 C. An oily layer then forms, which is separated from the aqueous phase by decantation. This oily layer has a volume of about 60 cc. It is analysed by vapour phase chromatography before and after being washed twice with half its volume of 1 1 water. The aqueous phase was worked up as described in the preceding examples.

The composition of the different phases is given in the following table:

We claim:

1. Process for the electrolytic hydrodimerisation of an alpha,beta-ethylenic compound which comprises subjecting to electrolysis in a single compartment cell a homogeneous aqueous solution of a pH 5 to 10 of said com- 12 pound and a quaternary ammonium salt of an oxygen containing inorganic acid having a pK in water of 5 to 11, the concentration of said quaternary ammonium salt being from 5 to 30% and the concentration of said alpha, beta-ethylenic compound :being 2.3 to 4.6% both by weight of solution.

2. Process according to claim 1, in which the a,fi-ethylenic compound is acrylonitrile.

References Cited UNITED STATES PATENTS 11/1969 Beck et a1 204-73 2/1970 Mihara et al 20473 U.S. Cl. X.R. 204-72 

